I had a friend do exactly this just a couple of weeks ago in NF - lost his blackberry down the gap between the raised bit where the table lives and the window.

In his case, as the phone was switched on in-flight (although with flight mode on), they insisted in getting the maintenance guys to take the seat apart to get the phone out as they said that in theory the plane would have to go out of service if a switched-on phone was known to be in the cabin on take-off.

It took the maintenance guys about 30 minutes to do this but he was reunited with his phone having waited in the cabin for them to retrieve it.

Good luck with lost property. I have never got anything back from them...